This invention relates to plasma devices for confining plasma at elevated temperatures and more particularly to plasma devices for generating power from neutron generating reactions. More specifically, the invention relates to structures which serve as both the first wall and blanket in the plasma device.
Plasma devices are frequently identified with fusion reactors used to confine plasma at elevated temperatures and to conduct experiments leading to nuclear fusion reactions. Considerable research and development work has been carried out in the past in the expectation that commercial units may be designed to generate power from neutron streams and other energy sources produced in the fusion reactions. Further background on these devices may be found in publications such as Fusion Reactor Physics, Principles and Technology by Terry Kanmash, Copyright 1975, by Ann Arbor Science Publishers, Inc.
In the designs for these devices, first wall structures are provided to form the first physical barrier for the plasma. The first wall is designed and constructed to withstand high particle and energy fluxes from the plasma, high thermal and mechanical stresses and elevated temperature operation. Also, the wall should not be a source of excessive plasma contamination. In addition to the first wall, blanket structures are included in the design to convert the fusion energy into sensible heat and provide for heat removal, to breed tritium and provide for tritium recovery and to provide some shielding for the magnet system. In the design and construction of the blanket, it is necessary that the blanket withstand high neutron fluences, elevated temperature operation, thermal and mechanical stresses, and be compatible with the chemical environment, the plasma and the vacuum. When necessary, a neutron multiplier is also present.
In some designs, as illustrated in FIG. 3, the first wall, neutron multiplier and blanket are separate parts constructed of different materials. In one design identified as STARFIRE, the blanket is constructed of a packed bed of particles (about 0.46 m thick) of .alpha.-LiAlO.sub.2 with stainless steel coolant tubes for head removal and passages through which helium may be fed for tritium removal. As indicated by the formula, .alpha.-LiAlO.sub.2 has a lithium atomic percentage of about 25%. Since .alpha.-LiAlO.sub.2 is essentially a ceramic material, its heat transfer properties are limited. In addition, as the concentration of lithium is reduced during the generation of tritium, it increases the probability of radiation damage and neutron leakage while decreasing the tritium production. Under these conditions, the useful life of the blanket becomes reduced and it may be necessary to replace the blanket on a more frequent schedule.
In addition to the problem with the life expectancy of the blanket, another problem relates to the limited heat transfer of the blanket. Other materials such as LiAl have been considered, however, they are not entirely satisfactory. To illustrate, LiAl is reactive with water. Therefore, new compositions for the blanket are desirable.
Accordingly, one object of the invention is a blanket for a plasma device which has a reduced rate of decrease in the lithium concentration. A second object of the invention is a process for replenishing lithium from which tritium may be generated. A third object of the invention is a composition for the blanket with an improved heat transfer. Another object of the invention is a composition for the blanket which is also useful for the first wall.